From 60d2934bcf87d20aefed25c48f68dfe604cec2ca Mon Sep 17 00:00:00 2001
From: Sergey Prokhorov <seriy.pr@gmail.com>
Date: Wed, 23 Nov 2022 01:34:31 +0100
Subject: [PATCH] Accept unexpected RPC packets from Telegram backend

---
 src/mtp_down_conn.erl | 6 +++++-
 src/mtp_rpc.erl       | 6 ++++--
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/mtp_down_conn.erl b/src/mtp_down_conn.erl
index 4579115..3ddb912 100644
--- a/src/mtp_down_conn.erl
+++ b/src/mtp_down_conn.erl
@@ -286,7 +286,11 @@ handle_rpc({close_ext, ConnId}, St) ->
             St1
     end;
 handle_rpc({simple_ack, ConnId, Confirm}, S) ->
-    up_send({simple_ack, self(), Confirm}, ConnId, S).
+    up_send({simple_ack, self(), Confirm}, ConnId, S);
+handle_rpc({unknown, Tag, Tail}, S) ->
+    ?log(info, "Unknown packet from backend. Tag ~p, tail: ~p", [Tag, Tail]),
+    S.
+
 
 -spec down_send(iodata(), #state{}) -> {ok, #state{}}.
 down_send(Packet, #state{sock = Sock, codec = Codec, dc_id = DcId} = St) ->
diff --git a/src/mtp_rpc.erl b/src/mtp_rpc.erl
index bd812ce..9562a37 100644
--- a/src/mtp_rpc.erl
+++ b/src/mtp_rpc.erl
@@ -86,7 +86,7 @@ encode_handshake({handshake, SenderPID, PeerPID}) ->
 
 %% It expects that packet segmentation was done on previous layer
 %% See mtproto/mtproto-proxy.c:process_client_packet
--spec decode_packet(binary()) -> packet() | error.
+-spec decode_packet(binary()) -> packet() | {unknown, binary(), binary()}.
 decode_packet(<<?RPC_PROXY_ANS, _AnsFlags:4/binary, ConnId:64/signed-little, Data/binary>>) ->
     %% mtproto/mtproto-proxy.c:client_send_message
     {proxy_ans, ConnId, Data};
@@ -94,7 +94,9 @@ decode_packet(<<?RPC_CLOSE_EXT, ConnId:64/signed-little>>) ->
     {close_ext, ConnId};
 decode_packet(<<?RPC_SIMPLE_ACK, ConnId:64/signed-little, Confirm:4/binary>>) ->
     %% mtproto/mtproto-proxy.c:push_rpc_confirmation
-    {simple_ack, ConnId, Confirm}.
+    {simple_ack, ConnId, Confirm};
+decode_packet(<<Tag:4/binary, Tail/binary>>) ->
+    {unknown, Tag, Tail}.
 
 
 encode_packet({data, Msg}, {{ConnId, ClientAddr, ProxyTag}, ProxyAddr}) ->